The behavior of wind farms when connected to the electrical grid system is becoming increasingly important for operation of wind farms. Because of the increasing number and size of the wind farms, they can and must make their contribution to ensuring the stability of the grid system. The important factors from the point of view of the grid system operators are not only the compensated feeding of real power, but there are additionally also requirements relating to the feeding of wattless component, in order to make it possible to comply with specific tolerance limits for the emitted voltage. The latter is particularly important in the case of wind farms which are connected to the medium-voltage grid system. This is because, in these grid systems, changes in the voltage level of individual points, such as the feed point of a large wind farm, due to the network structure, can lead to influences on the primary routes and directions in which the electrical power flows. It is also known for it to be highly important to feed in wattless components in order to support the voltage level. This is the case in particular in the event of a voltage dip.
The capability of wind farms with modern wind energy installations fitted with converters to feed both real power and a wattless component is therefore of major importance. One requirement is that specific nominal-value requirements must be complied with for the wattless component (irrespective of whether this relates to a direct requirement for the wattless component or the power factor), and frequently for the nominal voltage as well, with respect to a junction point between the wind farm and the grid system. The farm master uses these nominal value requirements to determine appropriate control signals for the individual wind energy installations in the wind farm. In doing so, it is necessary to remember that the wind energy installations in a wind farm do not necessarily all need to be identical, and that, particularly in spatially extended wind farms, they are frequently also connected via long lines with different capacitance and resistance characteristics. In order to counteract the delay effect associated with this, attempts have been made to transmit requirements for the voltage to be emitted by the wind energy installations, rather than wattless-component nominal values, to the wind energy installations, in which case the wind energy installations regulate this in accordance with the requirement by means of a local voltage regulator (DE-A-102004048339). This concept offers the advantage of rapid transmission, even when the transmission speed in the communication network is limited. However, it has disadvantageously been found that implementation can be difficult, particularly in the case of wind farms having wind energy installations of a different type or from different manufacturers. This applies in particular to retrofitting. It is also known for a dedicated wattless-component nominal value to be preset for each of the individual wind energy installations (WO-A-01/73518). One disadvantage of this concept is that, when the wattless component (or the power factor or the angle) of the individual wind energy installations is preset directly by the farm master, the limited transmission speeds in the communication network for the wind farm can result in delays, leading to delayed readjustment and thus to a poor response to rapid changes.